Anesthetic influence on arteriolar diameters and tissue oxygen tension in hemorrhaged rats

Arteriolar diameters and tissue oxygen tensions were measured in the cremaster muscles of 68 hemorrhaged rats which were anesthetized with either intramuscular ketamine, 125 mg/kg, plus 30 mg/kg supplements as needed, or enflurane, 2.2% inspired. Animals breathed room air, or room air plus enflurane, throughout the experiments. Arterioles in the cremaster muscle were identified according to successive orders of branching, and the internal diameters of first-, third-, and fourth-order vessels were measured at 30-s intervals. Cremaster muscle oxygen tension was measured polarographically with platinum-iridium microelectrodes. Mean arterial pressure was controlled at 30-35 mmHg during 30 min of hemorrhage, and maximum shed blood volumes were similar (2.6 ml/100 g) in both groups. Principal responses to hemorrhage in rats receiving enflurane were 1) constriction in first-, third-, and fourth-order arterioles, and 2) tissue hypoxia. In hemorrhaged rats receiving ketamine, the constrictor response to hemorrhage either was diminished (first-, and third-order arterioles) or abolished (fourth-order arterioles), and tissue hypoxia did not occur. The authors conclude that ketamine, as compared with enflurane, diminishes or prevents arteriolar constriction and tissue hypoxia in the cremaster muscle of hemorrhaged rats.